MDR1 causes resistance to the antitumour drug miltefosine

The anti-parasitic drug miltefosine suppresses activation of human eosinophils and ameliorates allergic inflammation in mice

BACKGROUND AND PURPOSE

Miltefosine is an alkylphosphocholine drug with proven effectiveness against various types of parasites and cancer cells. Miltefosine is not only able to induce direct parasite killing but also modulates host immunity, for example by reducing the severity of allergies in patients. To date, there are no reports on the effect of miltefosine on eosinophils, central effector cells involved in allergic inflammation.

EXPERIMENTAL APPROACH

We tested the effect of miltefosine on the activation of human eosinophils and their effector responses in vitro and in mouse models of eosinophilic migration and ovalbumin-induced allergic lung inflammation.

KEY RESULTS

The addition of miltefosine suppressed several eosinophilic effector reactions such as CD11b up-regulation, degranulation, chemotaxis and downstream signalling. Miltefosine significantly reduced the infiltration of immune cells into the respiratory tract of mice in an allergic cell recruitment model. Finally, in a model of allergic inflammation, treatment with miltefosine resulted in an improvement of lung function parameters.

CONCLUSION AND IMPLICATIONS

Our observations suggest a strong modulatory activity of miltefosine in the regulation of eosinophilic inflammation in vitro and in vivo. Our data underline the potential efficacy of miltefosine in the treatment of allergic diseases and other eosinophil-associated disorders and may raise important questions regarding the immunomodulatory effect of miltefosine in patients treated for leishmania infections.

Effects of a detergent micelle environment on P-glycoprotein (ABCB1)-ligand interactions

P-glycoprotein (P-gp) is a multidrug transporter that uses energy from ATP hydrolysis to export many structurally dissimilar hydrophobic and amphipathic compounds, including anticancer drugs from cells. Several structural studies on purified P-gp have been reported, but only limited and sometimes conflicting information is available on ligand interactions with the isolated transporter in a dodecyl-maltoside detergent environment. In this report we compared the biochemical properties of P-gp in native membranes, detergent micelles, and when reconstituted in artificial membranes. We found that the modulators zosuquidar, tariquidar, and elacridar stimulated the ATPase activity of purified human or mouse P-gp in a detergent micelle environment. In contrast, these drugs inhibited ATPase activity in native membranes or in proteoliposomes, with IC₅₀ values in the 10-40 nm range. Similarly, a 30-150-fold decrease in the apparent affinity for verapamil and cyclic peptide inhibitor QZ59-SSS was observed in detergent micelles compared with native or artificial membranes. Together, these findings demonstrate that the high-affinity site is inaccessible because of either a conformational change or binding of detergent at the binding site in a detergent micelle environment. The ligands bind to a low-affinity site, resulting in altered modulation of P-gp ATPase activity. We, therefore, recommend studying structural and functional aspects of ligand interactions with purified P-gp and other ATP-binding cassette transporters that transport amphipathic or hydrophobic substrates in a detergent-free native or artificial membrane environment.

Genomic and Molecular Characterization of Miltefosine Resistance in Leishmania infantum Strains with Either Natural or Acquired Resistance through Experimental Selection of Intracellular Amastigotes

During the last decade miltefosine (MIL) has been used as first-line treatment for visceral leishmaniasis in endemic areas with antimonial resistance, but a decline in clinical effectiveness is now being reported. While only two MIL-resistant Leishmania infantum strains from HIV co-infected patients have been documented, phenotypic MIL-resistance for L. donovani has not yet been identified in the laboratory. Hence, a better understanding of the factors contributing to increased MIL-treatment failure is necessary. Given the paucity of defined MIL-resistant L. donovani clinical isolates, this study used an experimental amastigote-selected MIL-resistant L. infantum isolate (LEM3323). In-depth exploration of the MIL-resistant phenotype was performed by coupling genomic with phenotypic data to gain insight into gene function and the mutant phenotype. A naturally MIL-resistant L. infantum clinical isolate (LEM5159) was included to compare both datasets. Phenotypically, resistance was evaluated by determining intracellular amastigote susceptibility in vitro and actual MIL-uptake. Genomic analysis provided supportive evidence that the resistance selection model on intracellular amastigotes can be a good proxy for the in vivo field situation since both resistant strains showed mutations in the same inward transporter system responsible for the acquired MIL-resistant phenotype. In line with previous literature findings in promastigotes, our data confirm a defective import machinery through inactivation of the LiMT/LiRos3 protein complex as the main mechanism for MIL-resistance also in intracellular amastigotes. Whole genome sequencing analysis of LEM3323 revealed a 2 base pair deletion in the LiMT gene that led to the formation an early stop codon and a truncation of the LiMT protein. Interestingly, LEM5159 revealed mutations in both the LiMT and LiRos3 genes, resulting in an aberrant expression of the LiMT protein. To verify that these mutations were indeed accountable for the acquired resistance, transfection experiments were performed to re-establish MIL-susceptibility. In LEM3323, susceptibility was restored upon expression of a LiMT wild-type gene, whereas the MIL-susceptibility of LEM5159 could be reversed after expression of the LiRos3 wild-type gene. The aberrant expression profile of the LiMT protein could be restored upon rescue of the LiRos3 gene both in the LEM5159 clinical isolate and a ΔLiRos3 strain, showing that expression of LdMT is dependent on LdRos3 expression. The present findings clearly corroborate the pivotal role of the LiMT/LiRos3 complex in resistance towards MIL.

Functional Validation of ABCA3 as a Miltefosine Transporter in Human Macrophages: IMPACT ON INTRACELLULAR SURVIVAL OF LEISHMANIA (VIANNIA) PANAMENSIS

Within its mammalian host, Leishmania resides and replicates as an intracellular parasite. The direct activity of antileishmanials must therefore depend on intracellular drug transport, metabolism, and accumulation within the host cell. In this study, we explored the role of human macrophage transporters in the intracellular accumulation and antileishmanial activity of miltefosine (MLF), the only oral drug available for the treatment of visceral and cutaneous leishmaniasis (CL). Membrane transporter gene expression in primary human macrophages infected in vitro with Leishmania Viannia panamensis and exposed to MLF showed modulation of ABC and solute liquid carrier transporters gene transcripts. Among these, ABCA3, a lipid transporter, was significantly induced after exposure to MLF, and this induction was confirmed in primary macrophages from CL patients. Functional validation of MLF as a substrate for ABCA3 was performed by shRNA gene knockdown (KD) in THP-1 monocytes. Intracellular accumulation of radiolabeled MLF was significantly higher in ABCA3(KD) macrophages. ABCA3(KD) resulted in increased cytotoxicity induced by MLF exposure. ABCA3 gene expression inversely correlated with intracellular MLF content in primary macrophages from CL patients. ABCA3(KD) reduced parasite survival during macrophage infection with an L. V. panamensis strain exhibiting low in vitro susceptibility to MLF. Confocal microscopy showed ABCA3 to be located in the cell membrane of resting macrophages and in intracellular compartments in L. V. panamensis-infected cells. These results provide evidence of ABCA3 as an MLF efflux transporter in human macrophages and support its role in the direct antileishmanial effect of this alkylphosphocholine drug.

Complex Interplay between the P-Glycoprotein Multidrug Efflux Pump and the Membrane: Its Role in Modulating Protein Function

Multidrug resistance in cancer is linked to expression of the P-glycoprotein multidrug transporter (Pgp, ABCB1), which exports many structurally diverse compounds from cells. Substrates first partition into the bilayer and then interact with a large flexible binding pocket within the transporter's transmembrane regions. Pgp has been described as a hydrophobic vacuum cleaner or an outwardly directed drug/lipid flippase. Recent X-ray crystal structures have shed some light on the nature of the drug-binding pocket and suggested routes by which substrates can enter it from the membrane. Detergents have profound effects on Pgp function, and several appear to be substrates. Biochemical and biophysical studies in vitro, some using purified reconstituted protein, have explored the effects of the membrane environment. They have demonstrated that Pgp is involved in a complex relationship with its lipid environment, which modulates the behavior of its substrates, as well as various functions of the protein, including ATP hydrolysis, drug binding, and drug transport. Membrane lipid composition and fluidity, phospholipid headgroup and acyl chain length all influence Pgp function. Recent studies focusing on thermodynamics and kinetics have revealed some important principles governing Pgp-lipid and substrate-lipid interactions, and how these affect drug-binding and transport. In some cells, Pgp is associated with cholesterol-rich microdomains, which may modulate its functions. The relationship between Pgp and cholesterol remains an open question; however, it clearly affects several aspects of its function in addition to substrate-membrane partitioning. The action of Pgp modulators appears to depend on their membrane permeability, and membrane fluidizers and surfactants reverse drug resistance, likely via an indirect mechanism. A detailed understanding of how the membrane affects Pgp substrates and Pgp's catalytic cycle may lead to new strategies to combat clinical drug resistance.

Imipramine is an orally active drug against both antimony sensitive and resistant Leishmania donovani clinical isolates in experimental infection

Background

In an endeavor to find an orally active and affordable antileishmanial drug, we tested the efficacy of a cationic amphiphilic drug, imipramine, commonly used for the treatment of depression in humans. The only available orally active antileishmanial drug is miltefosine with long half life and teratogenic potential limits patient compliance. Thus there is a genuine need for an orally active antileishmanial drug. Previously it was shown that imipramine, a tricyclic antidepressant alters the protonmotive force in promastigotes, but its in vivo efficacy was not reported.

Methodology/Principal Findings

Here we show that the drug is highly active against antimony sensitive and resistant Leishmania donovani in both promastigotes and intracellular amastigotes and in LD infected hamster model. The drug was found to decrease the mitochondrial transmembrane potential of Leishmania donovani (LD) promastigotes and purified amastigotes after 8 h of treatment, whereas miltefosine effected only a marginal change even after 24 h. The drug restores defective antigen presenting ability of the parasitized macrophages. The status of the host protective factors TNF α, IFN γ and iNOS activity increased with the concomitant decrease in IL 10 and TGF β level in imipramine treated infected hamsters and evolution of matured sterile hepatic granuloma. The 10-day therapeutic window as a monotherapy, showing about 90% clearance of organ parasites in infected hamsters regardless of their SSG sensitivity.

Conclusions

This study showed that imipramine possibly qualifies for a new use of an old drug and can be used as an effective orally active drug for the treatment of Kala-azar.

The disease Kala-azar or visceral leishmaniasis is still a big problem in the Indian subcontinent. The antimonials were used for the chemotherapy of Kala-azar but with time its efficacy has reduced dramatically. The newer version of orally active drug miltefosine has been introduced, but its efficacy has decreased considerably as relapse cases are on the rise. Other drugs like liposomal form of amphotericin B is expensive and the patients require hospitalization. Thus there is a genuine need for an orally active antileishmanial drug. There are reports that the cationic amphiphilic molecule, imipramine, a drug used for the treatment of depression in humans, kills the promastigotes of Leishmania donovani. We tested the efficacy of imipramine in experimental infection in hamster and mouse model. Our study showed that the drug is highly effective against antimony sensitive and antimony resistant Leishmania donovani infected hamsters as well as mouse and offered almost sterile cure.

Oleanolic acid derivative methyl 3,11-dioxoolean-12-en-28-olate targets multidrug resistance related to ABCB1

Multidrug resistance (MDR) in leukemia patients is a great incentive to the development of new drugs. In a search for potential multidrug resistance modulators we tested a group of oleanolic acid (OA) analogues modified at C-3, C-11, C-12 and C-28 using an experimental model consisting of three human acute lymphoblastic leukemia cell lines (CCRF-CEM and the multidrug resistant sublines CCRF-VCR1000 and CCRF-ADR5000). The most effective compound, methyl 3,11-dioxoolean-12-en-28-olate (DIOXOL) was more potent in cell viability inhibition than its precursor - OA, and showed similar or even higher activity in the drug resistant than in the wild-type cells. Resistance factor (RF) values obtained for CCRF-VCR1000 and CCRF-ADR-5000 cells using MTT assay were 0.7 and 0.8 (24 h of treatment) and after 72 h of treatment 0.9 and 1.1, respectively. Moreover, 5 μM DIOXOL significantly reduced the expression of the ABCB1 gene in MDR cells by around 30%, and also decreased the level of P-gp protein. Compared to untreated control cells, DIOXOL treatment resulted in a significant P-gp decrease (30% in CCRF-ADR5000 and 50% in CCRF-VCR1000), that was detected by western blot and confirmed by flow cytometry analysis. Moreover, DIOXOL (at 10 μM) significantly inhibited P-gp transport function by more than twofold comparing to control, untreated cells that was demonstrated using rhodamine 123-based functional test. The compound exhibited synergistic activity with ABCB1 substrate - adriamycin in CCRF-VCR1000 cells, indicating partial but significant MDR reversing ability.

Miltefosine: a review of its pharmacology and therapeutic efficacy in the treatment of leishmaniasis

Miltefosine is an alkylphosphocholine drug with demonstrated activity against various parasite species and cancer cells as well as some pathogenic bacteria and fungi. For 10 years it has been licensed in India for the treatment of visceral leishmaniasis (VL), a fatal neglected parasitic disease. It is the first and still the only oral drug that can be used to treat VL and cutaneous leishmaniasis (CL). The standard 28 day miltefosine monotherapy regimen is well tolerated, except for mild gastrointestinal side effects, although its teratogenic potential severely hampers its general use in the clinic and roll-out in national elimination programmes. The pharmacokinetics of miltefosine are mainly characterized by its long residence time in the body, resulting in extensive drug accumulation during treatment and long elimination half-lives. At the moment, different combination therapy strategies encompassing miltefosine are being tested in multiple controlled clinical trials in various geographical areas of endemicity, both in South Asia and East Africa. We here review the most salient pre-clinical and clinical pharmacological aspects of miltefosine, its mechanism of action against Leishmania parasites and other pathogens, and provide a systematic overview of the efficacy and safety data from all clinical trials of miltefosine, either alone or in combination, in the treatment of VL and CL.

Miltefosine induces apoptosis in arsenite-resistant Leishmania donovani promastigotes through mitochondrial dysfunction

The control of leishmaniasis in absence of vaccine solely depends on the choice of chemotherapy. The major hurdle in successful leishmanial chemotherapy is emergence of drug resistance. Miltefosine, the first orally administrable anti-leishmanial drug, has shown the potential against drug-resistant strains of Leishmania. However, there are discrepancies regarding the involvement of P-glycoprotein (Pgp) and sensitivity of miltefosine in multiple drug-resistant (MDR) cell lines that overexpress Pgp in Leishmania. To address this, the effect of miltefosine in arsenite-resistant Leishmania donovani (Ld-As20) promastigotes displaying an MDR phenotype and overexpressing Pgp-like protein was investigated in the current study. Results indicate that Ld-As20 is sensitive to miltefosine. Miltefosine induces process of programmed cell death in Ld-As20 in a time-dependent manner as determined by cell shrinkage, externalization of phosphatidylserine and DNA fragmentation. Miltefosine treatment leads to loss of mitochondrial membrane potential and the release of cytochrome C with consequent activation of cellular proteases. Activation of cellular proteases resulted in activation of DNase that damaged kinetoplast DNA and induced dyskinetoplasty. These data indicate that miltefosine causes apoptosis-like death in arsenite-resistant L. donovani.

Intestinal Absorption of Miltefosine: Contribution of Passive Paracellular Transport

PURPOSE

This study aimed to characterize the transepithelial transport of miltefosine (HePC), the first orally effective drug against visceral leishmaniasis, across the intestinal barrier to further understand its oral absorption mechanism.

MATERIALS AND METHODS

Caco-2 cell monolayers were used as an in vitro model of the human intestinal barrier. The roles of active and passive mechanisms in HePC intestinal transport were investigated and the relative contributions of the transcellular and paracellular routes were estimated.

RESULTS

HePC transport was observed to be pH-independent, partially temperature-dependent, linear as a function of time and non-saturable as a function of concentration. The magnitude of HePC transport was quite similar to that of the paracellular marker mannitol, and EDTA treatment led to an increase in HePC transport. Furthermore, HePC transport was found to be similar in the apical-to-basolateral and basolateral-to-apical directions, strongly suggesting that HePC exhibits non-polarized transport and that no MDR-mediated efflux was involved.

CONCLUSIONS

These results demonstrate that HePC crosses the intestinal epithelium by a non-specific passive pathway and provide evidence supporting a concentration-dependent paracellular transport mechanism, although some transcellular diffusion cannot be ruled out. Considering that HePC opens epithelial tight junctions, this study shows that HePC may promote its own permeation across the intestinal barrier.

P-glycoprotein (ABCB1) interacts directly with lipid-based anti-cancer drugs and platelet-activating factorsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease

The P-glycoprotein multidrug transporter (Pgp; ABCB1) is an ATP-binding cassette (ABC) protein that has been implicated in the multidrug resistance of human cancers. Pgp couples ATP hydrolysis to active extrusion from the cell of a broad array of amphipathic compounds via an ill-defined mechanism. Substrates are believed to interact with Pgp within the membrane. Reconstituted Pgp functions as an ATP-dependent flippase for a variety of fluorescently labelled membrane lipids. The protein may also function as a drug ‘flippase’, moving its substrates from the inner to the outer leaflet of the bilayer. We show that lipid-based anti-cancer drugs, such as miltefosine, and signaling molecules, such as platelet-activating factors, bind saturably to Pgp with Kd values in the low micromolar range, and modulate its ATPase activity. These compounds also inhibit Pgp-mediated flipping of fluorescent lipids and transport of Hoechst 33342 and tetramethylrosamine, which occupy different subsites in the drug-binding pocket. Bacterial lipid A modulates Pgp ATPase activity, and glycolipid flipping is inhibited by unlabelled glucosylceramide, suggesting that these lipids also interact with the transporter. These results indicate that Pgp treats a variety of lipid-based molecules as substrates, and likely interacts with lipids and drugs in the same manner.

New Insights into the Drug Binding, Transport and Lipid Flippase Activities of the P-Glycoprotein Multidrug Transporter

The MDR1 P-glycoprotein, an ATP-binding cassette (ABC) superfamily member that functions as an ATP-driven drug efflux pump, has been linked to resistance of human tumors to multiple chemotherapeutic agents. P-glycoprotein binds and actively transports a large variety of hydrophobic drugs and peptides. P-glycoprotein in reconstituted proteoliposomes is also an outwardly directed flippase for membrane phospholipids and simple glycosphinglipids. This review focuses on recent advances in our understanding of P-glycoprotein structure and function, particularly through the use of fluorescence spectroscopic approaches. Progress is being made towards understanding the structure of the transporter, especially the spatial relationship between the two nucleotide-binding domains. Exploration of the P-glycoprotein catalytic cycle using vanadate-trapped complexes has revealed that drug transport likely takes place by concerted conformational changes linked to relaxation of a high energy intermediate. Low resolution mapping of the protein using fluorescence resonance energy transfer showed that both the H and R drug-binding sites are located within the cytoplasmic leaflet. Two drugs can bind to the R-site simultaneously, suggesting that the protein contains a large flexible binding region.

Effects of miltefosine on membrane permeability and accumulation of [99mTc]-hexakis-2-methoxyisobutyl isonitrile, 2-[18F]fluoro-2-deoxy-d-glucose, daunorubucin and rhodamine123 in multidrug-resistant and sensitive cells

Miltefosine is a phospholipid analog that exhibits antineoplastic activity against breast cancer metastases, but its mechanism of action remains uncertain. The aim of this study was to investigate the transport mechanism for the removal of miltefosine and [99mTc]-hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) from multidrug-resistant cells. The P-glycoprotein pump function, cell viability, and 99mTc-MIBI and 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) uptakes were measured in NIH 3T3 (3T3) and NIH 3T3MDR1 G185 (3T3MDR1) mouse fibroblasts and human lymphoid B JY cells. Miltefosine treatment increased the permeability and fluidity of these tumor cells in a concentration-dependent manner. The multidrug-sensitive cells were 3-4 times more sensitive to miltefosine than the multidrug-resistant ones. The extent of 99mTc-MIBI accumulation in the P-glycoprotein-expressing cells increased in the presence of miltefosine, whereas the rhodamine123 and daunorubicin uptakes of the cells did not change significantly. In the 3T3MDR1 cells verapamil reinstated the rhodamine123 and daunorubicin accumulation, but not the 99mTc-MIBI uptake. Cyclosporin A reinstated the uptakes of 99mTc-MIBI, daunorubicin and rhodamine123 by the 3T3MDR1 cells. In a concentration-dependent manner miltefosine decreased the extents of 99mTc-MIBI, rhodamine123, daunorubicin and 18FDG accumulation in the JY and 3T3 cells. Our findings indicate a common transport mechanism for 99mTc-MIBI and miltefosine, which is distinct from that for rhodamine123 and daunorubicin in MDR cells.

Characterisation of Leishmania donovani promastigotes resistant to hexadecylphosphocholine (miltefosine)

Leishmania donovani promastigote lines resistant to hexadecylphosphocholine (HePC, miltefosine) at 2.5, 5.0, 10.0, 20.0 and 40.0 microM were developed in vitro by continuous step-wise drug pressure. The 40 microM line was 15 times more resistant to HePC than the wild-type clone and showed cross-resistance to the ether lipid ET-18-OCH3 (edelfosine) but not to the standard anti-leishmanial drugs. Resistance was stable up to 12 weeks in drug-free culture medium. No amplification of specific genes, including the multidrug resistance P-glycoprotein gene, could be detected in the resistant parasites.

In vivo and in vitro multitracer analyses of P-glycoprotein expression-related multidrug resistance

P-glycoprotein (Pgp) is an ABC (ATP binding cassette) transporter that is often overexpressed in tumours, contributing significantly to their multidrug resistance. In this study, we explored whether the radiotracers used in tumour diagnostics can be used for in vivo visualisation of Pgp-related multidrug resistance. We also examined the effects of different Pgp modulators on the accumulation of these radioligands in tumours with or without Pgp expression. In a SCID BC-17 mouse model, cells of the drug-sensitive KB-3-1 (MDR(-)) and the KB-V1 Pgp-expressing (MDR(+)) human epidermoid carcinoma cell lines were inoculated to yield tumours in opposite flanks. For in vivo scintigraphic (biodistribution) and positron emission tomography (PET) examinations, the mice were injected with technetium-99m hexakis-2-methoxybutylisonitrile ((99m)Tc-MIBI), carbon-11 labelled methionine and fluorine-18 fluoro-2-deoxy- d-glucose ((18)FDG). For validation, in vitro cell studies with (99m)Tc-MIBI,( 99m)Tc-tetrofosmin, [(11)C]methionine and (18)FDG were carried out using a gamma counter. The expression and function of the MDR product were proved by immunohistochemistry and spectrofluorimetry. (99m)Tc-MIBI uptake was significantly lower in KB-V1 cells as compared with KB-3-1-derived tumours in vivo (Pgp(+)/Pgp(-) =0.61+/-0.13; P<0.01) and cells in vitro (Pgp(+)/Pgp(-) =0.08+/-0.01; P<0.001).()Cyclosporin A reversed (99m)Tc-MIBI uptake in the Pgp+ cells, while verapamil failed to modify it. (18)FDG uptake was significantly higher in KB-V1 tumours (Pgp(+)/Pgp(-) =1.36+/-0.05; P<0.01) and cells (Pgp(+)/Pgp(- )=1.52+/-0.12; P<0.001). Whereas cyclosporin A eliminated the difference between FDG uptake in MDR(+) and MDR(-) cell lines, verapamil significantly increased it. When the animals were treated with verapamil, the ratio of (99m)Tc-MIBI uptake in the MDR(+) tumours to that in the MDR(-) tumours decreased to 0.38+/-0.05 ( P<0.01), while the ratio of (18)FDG uptake increased to 2.1+/-0.3 ( P<0.001). There were no significant differences in the [(11)C]methionine uptake in the MDR(+) and MDR(-) tumours and cell lines, nor was [(11)C]methionine accumulation modified by cyclosporin A. Parallel administration of (18)FDG and (99m)Tc-MIBI combined with verapamil treatment seems to be a good candidate as a non-invasive marker for the diagnosis of MDR-related Pgp expression in tumours.

Functional study of intracellular P-gp- and MRP1-mediated pumping of free cytosolic pirarubicin into acidic organelles in intrinsic resistant SiHa cells

We sought to determine the efficiency of the intracellular functional P-gp- and MRP1-mediated pumping of THP into acidic organelles in SiHa cells and etoposide-resistant SiHa/VP16 cells. The expression of both MDR1 and MRP1 genes of SiHa and SiHa/VP16 cells was clearly shown by using RT-PCR. The functional studies of both intracellular functional P-gp- and MRP1-mediated pumping were performed by using THP in a conventional spectrofluorometer, and they demonstrated that SiHa and SiHa/VP16 cells are good models to illustrate the functional role of intracellular P-gp and MRP1 in the transport of free cytosolic drug into acidic organelles. The functional P-gp and MRP1 proteins were identified both on plasma membranes and on intracellular vesicle membranes. Within the limit of experimental error, similar efficiencies in THP transport were observed in the two proteins at both locations in SiHa and SiHa/VP16 cells. The P-gp- and MRP1-mediated pump coefficient (k v a), Michealis-Menten's constant (K V m), and maximal pumping rate (V V max) values of those located on vesicular membranes were 1.87 +/- 0.30 pL x cell-1 x s-1, 1.63 +/- 0.21 microM, and 4.95 +/- 0.45 nM x s-1</sup>, respectively. Drug retention inside acidic organelles (C mon V) of SiHa cells was significantly higher than that of SiHa/VP16 cells, perhaps a consequence of slower movement of recycling endosomes and (or) lysosomes to the cell membrane of SiHa cells, leading to distended organelles and cell death. Our results suggest that intracellular P-gp and MRP1 proteins play an important role in the transport of free drug from cytosol to cytoplasmic acidic organelles.

Leishmania donovani resistance to miltefosine involves a defective inward translocation of the drug

Miltefosine (hexadecylphosphocholine [HePC]) is the first drug approved for the oral treatment of visceral leishmaniasis. As part of a study on the mechanisms of action of this drug and on the rates of resistance to this drug, we have been working in vitro with an Leishmania donovani line that was previously shown to be 15-fold more resistant to HePC. We have studied the accumulation of [(14)C]HePC by L. donovani promastigotes and have found a drastic reduction (>95%) in the ability of the resistant line to internalize the drug. Binding of HePC to the plasma membrane and drug efflux from preloaded cells were similar in both drug-sensitive and -resistant lines, and no [(14)C]HePC metabolism was evident in either line. Resistant parasites were also unable to take up other short-chain phospholipid analogs, independently of their polar head group, even though endocytosis remained unaltered. Finally, HePC uptake was temperature and energy dependent and sensitive to the thiol-reactive agent N-ethylmaleimide. We propose that inward translocation of a short-chain phospholipid across the plasma membrane may exist in Leishmania promastigotes and that such activity is defective in the resistant line.

Decrease of intestinal P-glycoprotein activity by 2n-propylquinoline, a new oral treatment for visceral leishmaniasis

Drugs currently available for visceral leishmaniasis treatment are potentially toxic, have to be administered by parenteral route and frequently give rise to drug resistance, due to the involvement of P-glycoproteins (P-gp) in Leishmania. The purpose of this study was to investigate a possible inhibitory effect of 2n-propylquinoline (2nPQ) on P-gp activity. 2nPQ is a new oral anti-leishmanial drug that has demonstrated its efficacy in BALB/c infected mice with Leishmania donovani [Antimicrob. Agents Chemother. 37 (1993) 859]. Rat everted gut sacs and human intestinal Caco-2 cell lines were used to study the effect of 2nPQ on P-gp activity. Our results demonstrate an inhibitory effect of 2nPQ on the P-gp activity with two P-gp substrates (rhodamine 123 and digoxin), two P-gp inhibitors (cyclosporin A and verapamil), and in two different species. Alone or associated with other active drugs, 2nPQ would be very useful to control Leishmania Multi-Drug-Resistance and intestinal P-gp in humans with kala-azar.

Choline transport in Leishmania major promastigotes and its inhibition by choline and phosphocholine analogs

Phosphatidylcholine is the most abundant phospholipid in the membranes of the human parasite Leishmania. The metabolic pathways leading to its biosynthesis are likely to play a critical role in parasite development and survival and may offer a good target for antileishmanial chemotherapy. Phosphatidylcholine synthesis via the CDP-choline pathway requires transport of the choline precursor from the host. Here, we report the first characterization of choline transport in this parasite, which is carrier-mediated and exhibits Michaelis-Menten kinetics with an apparent K(m) value of 2.5 microM for choline. This process is Na(+)-independent and requires an intact proton gradient to be fully functional. Choline transport into Leishmania is highly specific for choline and is inhibited by the choline carrier inhibitor hemicholinium-3, the channel blocker quinacrine, the antimalarial aminoquinolines quinine and quinidine, the antileishmanial phosphocholine analogs, miltefosine and edelfosine, and by choline analogs, most of which have antimalarial activities. Most importantly, choline analogs kill the promastigote form of the parasite in vitro in the low micromolar range. These results set the stage for the use of choline analogs in antileishmanial chemotherapy and shed new lights on the mechanism of action of the leishmanicidal phosphocholine analogs.

Effects of miltefosine on various biochemical parameters in a panel of tumor cell lines with different sensitivities

We investigated endocytosis activity, uptake of miltefosine (hexadecylphosphocholine), phospholipid and cholesterol content, the cell cycle, and apoptosis in 13 tumor cell lines (MCF7, MCF7/ADR, KB-3-1, KB-8-5, KB-C1, HeLa, HeLa-MDR1-G185, HeLa-MDR1-V185, CCRF/CEM, CCRF/VCR1000, CCRF/ADR5000, HL-60, HL-60/AR) with different sensitivities to treatment with the antitumor phospholipid analogues miltefosine and D-21266 (octadecyl-(N,N-dimethyl-piperidino-4-yl)-phosphate). In this panel of cell lines, MDR1 (multidrug resistance gene 1)- and MRP1 (multidrug resistance-associated protein)-expressing cells were found to be slightly more resistant to both compounds than sensitive parental cells. No correlation was found between resistance to miltefosine and endocytosis, intracellular concentration of miltefosine, the phospholipid and cholesterol content, induction of apoptosis, or cell cycle alterations in all the cell lines tested. Wild-type p53 containing WMN Burkitt's lymphoma cells and wild type p53-deficient CA46 exhibited similar sensitivities to miltefosine. The low percentage of apoptosis induced in MCF7 cells lacking caspase 3 indicated that caspase 3 seems to play an essential role in miltefosine-induced apoptosis.